JP7172268B2 - INKJET RECORDING DEVICE AND CONTROL METHOD OF INKJET RECORDING DEVICE - Google Patents

Description

The present invention relates to an inkjet recording apparatus and an inkjet recording apparatus control method.

In the ink jet recording apparatus, when ink is ejected from the head portion, if air bubbles are present in the ink, an ejection failure or the like occurs. For this reason, an inkjet recording apparatus has been proposed in which the ink is degassed by an ink degassing device before the ink is sent to the head portion (see, for example, Japanese Unexamined Patent Application Publication No. 2002-100001). In addition, an ink supply device for an inkjet recording apparatus has been proposed in which a cover is provided on the liquid surface of the ink in order to suppress the contact between the ink and the air in the ink tank (see, for example, Japanese Unexamined Patent Application Publication No. 2002-100002).

JP 2017-24217 A JP-A-08-216422

In the ink jet recording apparatus, the pressure in the head portion must be set to a negative pressure in order to control the meniscus in the head portion. Therefore, in the inkjet recording apparatus, it is required not only to deaerate the ink but also to bring the ink into contact with the atmosphere in the vicinity of the head to control the back pressure in the head. In an ink tank that performs such back pressure control, the ink comes into contact with the atmosphere, so the degassing degree of the ink in the ink tank decreases.

In order to solve the above-described problems, the present invention provides an inkjet recording apparatus capable of controlling the back pressure of an ink tank while suppressing a decrease in the degassing degree of ink, and a control method for the inkjet recording apparatus.

The inkjet recording apparatus of the present invention includes an ink degassing device for degassing ink, a head section for ejecting ink, and a prescribed range provided downstream of the ink degassing device to accommodate the supplied ink. and an ink tank for heating the ink in the ink tank, where B≦0.5A, where Acm ³ is the amount of ink in the ink tank, and Bcm ² is the contact area between the ink and the air at the amount A of ink. A heating section and a back pressure adjusting section for adjusting the back pressure of the ink in the ink tank are provided.

A control method for an ink jet recording apparatus according to the present invention comprises an ink degassing device for degassing ink, a head section for ejecting ink, and an ink degassing device provided downstream of the ink degassing device for containing ink. In an inkjet recording apparatus comprising a tank, an ink tank heating section for heating the ink in the ink tank, and a back pressure adjusting section for adjusting the back pressure of the ink in the ink tank, the amount of ink in the ink tank is is Acm ³ , and the contact area between the ink and the atmosphere at the ink amount A is Bcm ² , the amount of ink in the ink tank is controlled so that B≦0.5A.

According to the present invention, it is possible to provide an inkjet recording apparatus capable of controlling the back pressure of an ink tank while suppressing a decrease in the degassing degree of ink, and a control method for the inkjet recording apparatus.

It is a figure which shows schematic structure of an inkjet recording device. It is a bottom view of the nozzle surface of a head part. 2 is a block diagram of an ink supply system for supplying ink from an ink storage section to a head section in the inkjet recording apparatus; FIG. 3 is a diagram showing the configuration of an ink tank and its surroundings; FIG. 1 is a block diagram showing the functional configuration of an inkjet recording apparatus; FIG. 3 is a diagram showing the configuration of an ink tank and its surroundings; FIG. FIG. 7 is a top view of the ink tank shown in FIG. 6; 5 is a graph showing measurement results of the degree of ink degassing in Example 1. FIG. 3 is a table showing conditions of ink volume A (cm ³ ) and contact area B (cm ² ) between the ink and air in Example 2. FIG. 10 is a table showing measurement results of the degree of ink degassing in Example 2. FIG. 7 is a graph showing the measurement results of the degree of ink degassing in Example 2. FIG. 10 is a graph showing the measurement results of the degree of ink degassing in Example 3. FIG. 10 is a graph showing the measurement results of the degree of ink degassing in Example 4. FIG.

Examples of embodiments for carrying out the present invention will be described below, but the present invention is not limited to the following examples.
The description will be given in the following order.
1. Embodiment of Inkjet Recording Apparatus (First Embodiment)
2. Embodiment of Inkjet Recording Apparatus (Second Embodiment)

<1. Embodiment of Inkjet Recording Apparatus>
A first embodiment of the inkjet recording apparatus of the present invention will be described below.
FIG. 1 shows a schematic configuration of an inkjet recording apparatus.

[Configuration of Inkjet Recording Apparatus]
The inkjet recording apparatus 100 shown in FIG. 1 has a line head, and a color image is formed by ejecting ink of a plurality of colors (here, four colors) at appropriate timing while moving the recording medium with respect to the line head. This is a one-pass type recording apparatus that forms a recording medium.

The inkjet recording apparatus 100 includes a medium supply section 10, an image forming main section 20, a medium discharge section 30, an ink storage section 50, and a control section 40 (see FIG. 5). In the inkjet recording apparatus 100, the recording medium P stored in the medium supply section 10 is transported to the image forming main section 20 under the control of the control section 40, and after an image is formed, the recording medium P is discharged to the medium discharge section 30. be.

(Medium supply unit)
The medium supply unit 10 feeds the recording medium P stored inside to the image forming main unit 20 one by one. As the recording medium P, in addition to printing paper, various media such as cells, films, and fabrics, which can be curvedly carried on the outer peripheral surface of the image forming drum 22, are used.

The medium supply unit 10 has a supply tray 11 that stores the recording medium P and a feeder board 12 that conveys the recording medium P from the supply tray 11 to the image forming main unit 20 . The medium supply unit 10 also has a supply unit (not shown) that transfers the uppermost recording medium P placed on the supply tray 11 onto the belt 123 .

The supply tray 11 is a plate-like member on which one or more recording media P can be placed. The supply tray 11 is provided to move up and down according to the amount of recording media P placed on the supply tray 11 .
The feeder board 12 comprises rollers 121 and 122 provided inside, and a ring-shaped belt 123 suspended between the rollers 121 and 122 . The feeder board 12 drives the rollers 121 and 122 to convey the recording medium P delivered from the supply unit onto the belt 123 along the belt 123 .

(Image forming main unit)
The image forming main unit 20 includes a delivery unit 21 , an image forming drum 22 , a head unit 23 , an irradiation unit 24 and a delivery unit 25 .

The transfer unit 21 transfers the recording medium P transferred from the medium supply section 10 to the image forming drum 22 . The transfer unit 21 has a swing arm portion 211 and a transfer drum 212 . The swing arm portion 211 carries one end of the recording medium P conveyed from the feeder board 12 . Then, the delivery drum 212 delivers the recording medium P carried by the swing arm portion 211 to the image forming drum 22 .

The image forming drum 22 has a cylindrical outer shape, carries the recording medium P on the outer peripheral surface of the cylindrical portion, and conveys the recording medium P according to the rotational movement about the central axis of the cylinder. A drum heater 221 for heating the outer peripheral surface and the recording medium P is provided near the outer peripheral surface of the image forming drum 22 . The drum heater 221 is positioned, for example, in the rotation direction of the image forming drum 22 between the transfer position of the recording medium P to the image forming drum 22 by the transfer unit 21 and the image recording position on the recording medium P by the head section 23 . be provided. The heating operation time and intensity of the drum heater 221 are controlled based on the temperature of the outer peripheral surface of the image forming drum 22 measured by a temperature measuring unit (not shown) so that the temperature of the recording medium P carried by the drum heater 221 reaches an appropriate temperature. As a result, when the ink lands on the recording medium P, the curing speed and the like of the recording medium P can be appropriately maintained, and a high-quality image can be stably formed. For the drum heater 221, for example, an infrared heater or a heating wire that generates heat when energized is used. The drum heater 221 may be provided inside the image forming drum 22 and heat the outer peripheral surface by thermal conduction.

The head unit 23 has a plurality of nozzle openings provided on a surface (nozzle surface) of the recording medium P facing the recording target surface. The head unit 23 ejects ink droplets from the nozzle openings at appropriate timings onto the recording surface of the recording medium P, which moves according to the rotation of the image forming drum 22, onto the recording target surface of the recording medium P. An image is formed by making it land.

FIG. 2 shows a bottom view of the nozzle surface of the head portion 23. As shown in FIG. The head section 23 shows an example in which eight inkjet heads 230 are arranged in a houndstooth pattern. The inkjet heads 230 are arranged with overlap in the width direction perpendicular to the conveying direction of the recording medium P. As shown in FIG. As a result, by moving the recording medium P in the conveying direction while the head unit 23 is fixed, an image can be recorded in the entire width direction of the recording medium P, thereby enabling image recording by a one-pass method.

In addition, the inkjet recording apparatus 100 shown in FIG. 1 includes a plurality of head units 23 at predetermined intervals in the conveying direction of the recording medium P. As shown in FIG. FIG. 1 shows an example in which four head units 23 are provided for each of four colors of ink. The four head units 23 output Y (yellow), M (magenta), C (cyan), and K (black) inks, for example. As these inks, for example, various well-known inks that undergo a phase change from a gel state to a sol state by being heated from room temperature and are cured by being irradiated with ultraviolet rays are used. Further, the ink supplied to the image forming main unit 20 is maintained at an appropriate temperature by a heating unit (not shown).

The irradiation unit 24 irradiates energy rays of a predetermined wavelength, for example, ultraviolet rays in a near-ultraviolet region (wavelength of about 400 nm) to cure the ink ejected from the head unit 23 and landed on the recording medium P. The formed image is fixed. The irradiation unit 24 includes, for example, a light emitting diode (LED) that emits ultraviolet rays, a mercury lamp, or the like as an irradiation source. A voltage is applied to the irradiation unit 24 by driving the irradiation drive unit 74 (see FIG. 5), and the ink on the recording medium P is irradiated with ultraviolet rays. The irradiation unit 24 is provided downstream of the head unit 23 in the rotation direction of the image forming drum 22 and upstream of the recording medium P delivered to the delivery unit 25 . Further, in the irradiation unit 24, a light shielding plate 241 is provided at a position covering the irradiation source and the set range of the ultraviolet rays in order to reduce the amount of the ultraviolet rays leaking outside the set range in which the recording medium P is irradiated with the ultraviolet rays. there is

The configuration of the irradiation source that emits ultraviolet light in the irradiation unit 24 is not particularly limited. If the ink has the property of being cured by receiving energy rays other than ultraviolet rays, a well-known irradiation source that emits energy rays of a wavelength that cures the ink is provided instead of the above-described configuration that emits ultraviolet rays.

The delivery section 25 conveys the recording medium P after the image formation is completed by curing the landed ink to the medium discharge section 30 . The delivery section 25 includes a cylindrical transfer roller 251, a plurality (for example, two) of rollers 252 and 253, a loop belt 254 carried by the rollers 252 and 253, and the like. The transfer roller 251 receives the recording medium P from the image forming drum 22 and guides it onto the belt 254 . The delivery unit 25 conveys the recording medium P delivered from the delivery roller 251 onto the belt 254 by moving it together with the belt 254 that circulates with the rotation of the rollers 252 and 253, and delivers it to the medium ejection unit 30. .

The medium ejecting section 30 stores the recording medium P delivered from the image forming main body section 20 by the delivery section 25 until it is taken out by the user. The medium ejection section 30 has a plate-shaped ejection tray 31 on which the recording medium P after image formation is placed.

The control unit 40 (see FIG. 5) controls the operations of the medium supply unit 10, the image forming main unit 20, the ink storage unit 50, and the medium discharge unit 30, and outputs image data and an image to be formed according to an image forming command (job). An image is formed on the recording medium P according to the setting related to formation.

The ink storage section 50 stores ink of each color used for image recording, and supplies the ink to the head section 23 (inkjet head 230 ) of the image forming body section 20 . Each component of the ink storage unit 50 is not particularly limited, but for example, it is arranged in a dedicated rack or the like and connected to the image forming main unit 20 via a tubular member such as a tube.

[Ink Supply System of Inkjet Recording Apparatus]
In the inkjet recording apparatus 100, ink is supplied from the ink storage section 50 to the head section 23 through the ink flow path. FIG. 3 shows a block diagram of an ink supply system for supplying ink from the ink storage section 50 to the head section 23 in the inkjet recording apparatus 100. As shown in FIG.

As shown in FIG. 3 , the ink supply system of the inkjet recording apparatus 100 includes an ink reservoir 50 , an ink degassing device 29 , an ink tank 26 and a head section 23 . Further, in the inkjet recording apparatus 100, a plurality of head units 23 are provided for each of the plurality of ink types described above, and each head unit 23 supplies ink corresponding to each ink type via an independent ink supply system. Ink is supplied from the reservoir 50 .

Further, the inkjet recording apparatus 100 includes a first ink feeding section 51 including a pump or the like for feeding ink from the ink storage section 50 to the ink degassing device 29 , and ink from the ink degassing device 29 to the ink tank 26 . and a second ink feeding unit 52 including a pump or the like for feeding the ink. Note that the inkjet recording apparatus 100 is provided with a gas flow path for adjusting the pressure of ink and air in the ink flow path. The ink flow path and gas flow path as described above constitute the first ink liquid feeding section 51 and the second ink liquid feeding section 52 for supplying ink to the head section 23 .

The ink tank 26 is a tank having a capacity smaller than that of the ink reservoir 50, and is configured as a sealed container that appropriately stores the ink contained in the ink reservoir 50. As shown in FIG.
An ink degassing device 29 is provided between the ink reservoir 50 and the ink tank 26, and the ink degassing device 29 removes air bubbles and dissolved gases from the ink sent from the ink reservoir 50 to the ink tank 26. Perform degassing. The ink degassing device 29 has, for example, a large number of hollow fiber membranes, and the air in the ink is removed by bringing the ink into contact with the outer surface of the hollow fiber membranes while evacuating the inside of the hollow fiber membranes with a vacuum pump. Suction inside the hollow fiber membrane.

The inkjet recording apparatus 100 includes a back pressure adjusting section 27 connected to the ink tank 26 , and the back pressure in the ink tank 26 is controlled by the back pressure adjusting section 27 . The back pressure adjusting unit 27 includes a back pressure valve (not shown) connected to the ink tank 26 via a gas flow path, an air tank, a back pressure pump connected to the air tank, and the like. The back pressure adjusting unit 27, for example, opens a back pressure valve to allow the ink tank 26 and the air tank to communicate with each other through the gas flow path. Then, the pressure (air pressure) in the ink tank 26 is adjusted by driving the back pressure pump to reduce the pressure (air pressure) in the air tank (negative pressure).

The inkjet recording apparatus 100 also includes a degassing device heating section 53, an ink tank heating section 54, and a head heating section 55, and the ink degassing device 29, the ink tank 26, and the head section 23 are respectively It is heated by a device heating section 53, an ink tank heating section 54, and a head heating section 55, and is controlled to reach a predetermined temperature.

[Ink tank configuration]
FIG. 4 shows the configuration of the ink tank 26 and its surroundings. Ink sent from the ink degassing device 29 via the second ink liquid sending section 52 is stored in the ink tank 26 . The ink stored in the ink tank 26 is kept at a predetermined temperature by the ink tank heating section 54 . Further, the ink stored in the ink tank 26 is transported to the head section 23 and ejected from the head section 23 according to the print job.

A liquid level sensor 56 is provided on the upper surface of the ink contained in the ink tank 26 (interface between ink and air) as an ink amount detection unit for detecting the amount of ink in the ink tank 26 . . A known sensor can be used as the liquid level sensor 56 . For example, in the ink tank 26, level switches for detecting the presence or absence of ink are arranged at positions corresponding to the upper and lower limits of the ink, or a liquid level switch for measuring the amount of ink in the ink tank 26 as a continuous value. A configuration in which an area meter is arranged may be used. These liquid level sensors 56 include a float sensor that detects the liquid level based on the position of the float, an ultrasonic sensor that measures the reflection of ultrasonic waves on the liquid level, and a liquid level based on the dielectric constant difference between gas and liquid. and a pressure sensor for detecting the weight and pressure of the liquid at the bottom of the tank.

In the ink tank 26, a back pressure adjusting section 27 is connected via a gas flow path to a cavity above the stored ink. In the ink tank 26 , the pressure inside the cavity above the ink is controlled by the operation of the back pressure adjusting section 27 . Thereby, the back pressure control in the head part 23 can be performed. For example, on the nozzle surface of the head unit 23, a pressure difference is generated between the normal ink pressure (that is, a state in which no pressure is applied to eject ink) and the atmospheric pressure, thereby eliminating the need for ink from the nozzles. leakage can be suppressed. In addition, the back pressure in the head section 23 can be adjusted so that the ink is appropriately ejected according to the pressure pattern applied when the ink is ejected.

The ink tank 26 satisfies B≦0.5A, where Acm ³ is the amount (volume) of ink held in the ink tank 26 within a specified range, and Bcm ² is the contact area between the ink and the air at the ink amount A. formed to meet When the inkjet recording apparatus is driven, the ink is fed from the ink tank 26 to the head unit 23, and the ink is fed from the ink storage unit 50 to the ink tank 26, so that the upper limit value of the ink tank 26 is to the lower limit is stored in the ink tank 26 . Therefore, the ink amount (volume) ^Acm3 within the specified range in the ink tank 26 can be the ink amount between the upper limit and the lower limit of the ink tank 26 .

In the ink tank 26 provided on the downstream side of the ink degassing device 29, the degassing degree of the ink decreases due to contact between the ink and the air. In particular, when the inkjet recording apparatus 100 has a configuration such as the ink tank heating unit 54 that promotes the convection of the ink in the ink tank 26, the atmosphere easily dissolves in the ink, and the degassing degree of the ink decreases. easy to decline. In the ink tank 26, in order to suppress the decrease in the degassing degree of the ink, it is necessary to prevent contact between the ink and the atmosphere in the ink tank 26, or to limit the contact area between the ink and the atmosphere to be small. is preferred.

On the other hand, in the inkjet recording apparatus 100, it is necessary to connect the back pressure adjusting section 27 to the cavity above the ink tank 26 and adjust the pressure in the cavity to perform meniscus control of the ink in the head section 23. . That is, in order to control the back pressure in the ink tank 26, it is necessary to bring the ink into contact with the atmosphere within the ink tank 26. FIG. For this reason, in the inkjet recording apparatus 100, it is necessary to limit the contact area between the ink and the air in the ink tank 26, thereby suppressing the decrease in the degree of degassing and controlling the back pressure.

[Functional Configuration of Inkjet Recording Apparatus]
FIG. 5 is a block diagram showing the functional configuration of the inkjet recording apparatus 100 of this embodiment. 1 to 4 are used together with the configuration and symbols shown in FIG. 5 as necessary in the following description.

As described above, the inkjet recording apparatus 100 includes the first ink feeding section 51, the second ink feeding section 52, the ink degassing device 29, the back pressure adjusting section 27, the liquid level sensor 56, and the degassing unit. It includes an air device heating section 53 , an ink tank heating section 54 and a head heating section 55 . The inkjet recording apparatus 100 also includes a control section 40 , a transport drive section 71 , a head drive section 731 , an irradiation drive section 74 , a communication section 61 , an operation display section 62 and a bus 69 . A bus 69 is a path for electrically connecting each component to exchange signals.

The control unit 40 centrally controls the overall operation of the inkjet recording apparatus 100 . The control unit 40 includes a CPU 41 (Central Processing Unit), a RAM 42 (Random Access Memory), a ROM 43 (Read Only Memory), and a memory 44 .
The CPU 41 performs various arithmetic processing according to a program read from the ROM 43, and performs operations such as transportation of the recording medium in the inkjet recording apparatus 100, opening and closing of each valve, feeding of ink by each pump, and ejection of ink. control. In addition, the CPU 41 performs various processes related to image recording based on image data, status signals and clock signals of each section according to programs read from the ROM 43 . The RAM 42 provides working memory space to the CPU 41 and stores temporary data. The ROM 43 stores control programs, initial setting data, and the like. In addition, the ROM 43 includes a non-volatile memory or the like that can be overwritten and updated, and can store setting data or the like that is set and maintained at any time. A memory 44 is an image memory that temporarily stores image data to be recorded.

The transport drive unit 71 generates a drive signal for rotating each roller in an appropriate direction and speed for driving the rotation motor of the image forming drum 22 and the feeder board 12 and the delivery unit 25 . Based on the control signal from the control unit 40, the transport drive unit 71 outputs a drive signal corresponding to the rotation direction and rotation speed of each motor.

The first ink liquid feeding section 51 and the second ink liquid feeding section 52 are pumps arranged in the ink conveying path between the ink storage section 50 and the ink tank 26 based on the control signal from the control section 40 . , the ink is sent from the ink reservoir 50 to the ink tank 26 via the ink degassing device 29 . When the ink is sent from the ink reservoir 50 to the ink tank 26 , the ink is degassed before reaching the ink tank 26 by passing through the ink degassing device 29 . Therefore, the ink tank 26 contains degassed ink.

The head driving unit 731 generates and outputs a driving voltage signal for deforming (performing a driving operation) the pressure chambers (piezoelectric elements) in order to properly eject ink from each nozzle of the inkjet head 230 . . Based on the control signal from the control unit 40, the head driving unit 731 selects a voltage waveform pattern stored in advance to generate a driving voltage signal that is power-amplified, and according to the image data input from the memory 44. It switches whether or not to output a driving voltage signal to each piezoelectric element.

The ink tank heating unit 54 heats and maintains the ink in the ink tank 26 at an appropriate temperature, thereby maintaining the ink in the ink tank 26 in a sol state. In addition, the head heating section 55 heats and maintains the ink at an appropriate temperature in the head section 23 of the image forming main body section 20 or the like, thereby maintaining the viscosity of the ink at the time of ejection in an appropriate state. The degassing device heating unit 53 heats and maintains the ink at an appropriate temperature in the ink degassing device 29, thereby maintaining the viscosity, temperature, saturated dissolved oxygen concentration, etc. of the ink at the time of degassing in an appropriate state. . The temperature of the ink in the ink degassing device 29 , the head section 23 and the ink tank 26 is measured by a temperature measuring section or the like arranged in each configuration and output to the control section 40 . The control unit 40 controls the operation states of the ink tank heating unit 54, the head heating unit 55, and the deaerator heating unit 53, and the temperature of the ink in the ink deaerator 29, the head unit 23, and the ink tank 26 is adjusted.

The liquid level sensor 56 detects the amount of ink in the ink tank 26 and outputs a detection signal to the controller 40 . The liquid level sensor 56 detects the amount of ink in the ink tank 26 by, for example, measuring the height of the ink level in the ink tank 26 . Ink is supplied from the ink reservoir 50 to the ink tank 26 according to the amount of ink in the ink tank 26 detected by the liquid level sensor 56 , and an appropriate amount of ink is maintained in the ink tank 26 . As a result, when the ink amount (volume) within the specified range of the ink tank 26 is Acm ³ and the contact area between the ink and the atmosphere at the ink amount A is Bcm ² , the ink is supplied so as to satisfy B≦0.5A. A suitable amount of ink is maintained in tank 26 .

Further, the liquid level sensor 56 outputs the measurement result of the amount of ink in the ink tank 26 to the control section 40 . The controller 40 acquires the amount of ink in the ink tank 26 based on the output from the liquid level sensor 56 . The controller 40 adjusts the amount of ink supplied from the ink reservoir 50 to the ink tank 26 based on the acquired amount of ink in the ink tank 26 . As a result, when the ink amount (volume) within the specified range in the ink tank 26 is Acm ³ , and the contact area between the ink and the atmosphere at the ink amount A is Bcm ² , B≦0.5A is satisfied. Control to maintain the amount of ink in the ink tank 26 can also be performed.

The back pressure regulator 27 controls the opening and closing of the back pressure valve according to the control signal from the controller 40 . Further, the drive of the back pressure pump is controlled by the control signal from the control unit 40, and the pressure (air pressure) in the air tank is controlled to a predetermined pressure (negative pressure).

The irradiation drive unit 74 applies a predetermined voltage to the irradiation source of the irradiation unit 24 in accordance with a control signal from the control unit 40 to cause current to flow and cause the irradiation source to emit energy rays of a predetermined wavelength.
The communication unit 61 is a communication interface that controls communication operations with external devices. The communication interface includes, for example, a LAN board, a LAN card, etc., which are compatible with various communication protocols. The communication unit 61 acquires image data to be recorded and setting data (job data) related to image recording from an external device under the control of the control unit 40, and also transmits status information and the like to the external device.

The operation display unit 62 displays the status of the inkjet recording apparatus 100 and an operation menu according to a control signal from the control unit 40 , and also receives an input operation from the outside such as a user and outputs the input operation to the control unit 40 . The operation display unit 62 includes, for example, a liquid crystal display unit in which a touch sensor as operation reception means overlaps with a display screen as display means. The control unit 40 causes the liquid crystal display unit to display status and various menus for receiving commands by the touch sensor, and displays information on the content and position of the displayed menu and the user's touch operation detected by the touch sensor. A control operation is performed to cause each unit of the inkjet recording apparatus 100 to perform corresponding processing.

<2. Embodiment of Inkjet Recording Apparatus (Second Embodiment)>
Next, a second embodiment of the inkjet recording apparatus will be described. The inkjet recording apparatus of the second embodiment can employ the same configuration as that of the above-described first embodiment, except for the configuration of the liquid level sensor arranged in the ink tank. For this reason, in the following description, the description that overlaps with the first embodiment will be omitted, and the configuration of the ink tank in which the liquid level sensor is arranged will be mainly described.

[Ink tank configuration]
FIG. 6 shows the configuration of the ink tank 26 and its surroundings of the ink jet recording apparatus of the second embodiment. 7 shows a top view of the ink tank 26 shown in FIG. Note that the same configurations as those shown in FIGS. 1 to 3 can be applied to the overall configuration of the inkjet recording apparatus and the ink supply system in the inkjet recording apparatus.

In the ink jet recording apparatus having the configuration shown in FIG. 6, ink is fed from the ink reservoir 50 into the ink tank 26 through the ink degassing device 29 in the same manner as in the ink jet recording apparatus of the first embodiment. The ink stored in the ink tank 26 is kept at a predetermined temperature by the ink tank heating section 54 . Further, the ink stored in the ink tank 26 is sent to the head section 23 and ejected from the head section 23 according to the print job.

The ink tank 26 shown in FIGS. 6 and 7 has an air blocking portion for partially blocking contact between the ink and the air. FIG. 6 and FIG. 7 show an example of an air shielding section that includes a cover member 58 that covers the upper surface of the ink contained in the ink tank 26 (the interface between the ink and the air). The lid member 58 preferably has a float that floats on the upper surface of the ink due to buoyancy. Note that the air blocking portion is not limited to the cover member 58, and the configuration such as the shape and material is not limited as long as the contact between the ink 57 and the atmosphere can be prevented in the ink tank 26. FIG. Further, the configuration such as the shape and material of the lid member 58 can be appropriately selected according to the shape of the ink tank 26, the physical properties of the ink, and the like. As long as the float can float on the ink in the ink tank 26 and can prevent contact between the ink 57 and the atmosphere, there are no restrictions on the configuration such as shape and material.

As shown in FIG. 7, in the portion of the ink tank 26 where the lid member 58 (float) floats, the lid member 58 largely blocks contact between the ink 57 and the atmosphere. Therefore, the portion where the ink 57 mainly contacts the atmosphere is limited to the portion where the upper surface of the ink 57 is exposed between the cover member 58 and the wall surface of the ink tank 26 .
Thus, in the ink tank 26, since the cover member 58 is present on the ink 57, the cover member 58 prevents the ink 57 from coming into contact with the atmosphere. Limited contact area.

In the inkjet recording apparatus of the second embodiment, the portion where the upper surface of the ink 57 is exposed can be limited by adjusting the size of the air blocking portion such as the lid member 58 . Therefore, by adjusting the size of the air blocking portion and limiting the area B (cm ² ) of the contact surface between the ink 57 exposed from the air blocking portion and the air, the ink is accommodated in the ink tank 26 . The ink tank 26 that satisfies B≦0.5A with respect to the volume A (cm ³ ) of the ink 57 can be easily realized regardless of the shape, volume, or the like.

Further, in the ink jet recording apparatus of the second embodiment, it is preferable that the lid member 58 constituting the air shielding portion is a part of the liquid level sensor 56 . For example, it is preferable that the liquid level sensor 56 is a float sensor and the float of the float sensor is the lid member 58 . Since the cover member 58 constitutes the liquid level sensor 56, the contact between the ink 57 and the atmosphere can be limited by the liquid level sensor 56, so that additional configuration within the ink tank 26 is not required. The float sensor may be of any type as long as it has a float that floats on the ink contained in the ink tank 26 by buoyancy.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these.

[Example 1: Decrease in degassing degree of ink due to contact area]
As described in each of the above-described embodiments, when the ink is stored in the ink tank for a long period of time in contact with the air, the degassing degree of the ink decreases. This decrease in the degassing degree of the ink is affected by the ratio between the ink volume A (cm ³ ) in the ink tank and the contact area B (cm ² ) between the ink and the atmosphere. Further, the longer the ink stays in the ink tank, the lower the degree of ink degassing. Therefore, ink tanks containing ink are prepared so that the ratio between the ink volume A (cm ³ ) and the contact area B (cm ² ) are different, and the degree of degassing of the ink in the ink tank decreases over time. was measured.

The deaeration degree of the ink was measured under the following conditions.
A piezo head as the head portion 23, a pump as the first ink feeding portion 51 and the second ink feeding portion 52, an ink capacity of the ink reservoir 50 of 25000 cm ³ , an ink capacity of the ink degassing device 29 of 300 cm ³ , and an ink tank. 26, an ink jet recording apparatus 100 (see FIG. 3) having an ink capacity of 60 cm ³ was prepared. In addition, a degassing device using a vacuum pump and a hollow fiber membrane was used as an ink degassing device, and the vacuum pump was controlled at about -98 kPa to degas the ink. A back pressure pump having a pressure sensor was used as the back pressure adjusting unit 27, and the back pressure in the ink tank was controlled at -2 kPa according to the pressure value of the pressure sensor. Gel ink (a phase change ink that changes from gel to sol at a predetermined temperature) was used as the ink.

In the apparatus having the above configuration, the ratio of the contact area B (cm ² ) between the ink and the air to the ink amount A (cm ³ ) in the ink tank is B=0.2 A cm ² , B=0.3 A cm ² , B= The amount of ink in the ink tank was adjusted to 0.5 Acm ² , B=0.7 Acm ² and B=0.9 Acm ² .

Furthermore, in the ink jet recording apparatus described above, assuming that the power supply was kept on for one week without consuming ink, the ink degassing device 29, the ink tank, and the ink in the head section were heated at 80°C. Hold for 7 days. Then, the degassing degree of the ink in the ink tank was measured every day. In general, if the degree of degassing can be maintained at 80% or more, it is considered to be within a practically acceptable range.
The degassing degree of the ink was calculated using the following formula.
Degree of degassing (%) = [1-(dissolved oxygen content in ink/saturated dissolved oxygen content at measurement temperature)] x 100

The degree of degassing was measured by dissolved oxygen concentration. The dissolved oxygen concentration can be measured by, for example, the Ostwald method (Experimental Chemistry Course 1 Basic Operation [I], page 241, 1975, Maruzen), a method of measuring by a mass spectrum method, or a simple method such as a galvanic cell type or a polarographic type. It can be measured using an oximeter or a colorimetric analysis method. Further, the dissolved oxygen concentration may be measured using a commercially available dissolved oxygen concentration meter (DO-30A type manufactured by Toa Denpa Kogyo Co., Ltd.).

FIG. 8 shows the measurement results of the degree of ink degassing.
As shown in FIG. 8, under any conditions in which the ratio of the contact area B (cm ² ) between the ink and air to the ink amount A (cm ³ ) is changed, the degree of ink degassing decreases over time. Further, the larger the contact area between the ink and the air in the ink tank, the larger the degassing rate in the ink.

Under the above conditions, by setting the contact area B (cm ² ) between the ink and the atmosphere to 0.5 A cm ² or less, the degree of degassing of the ink after holding for 7 days is 80%, which is considered to be a practically acceptable range. We are able to maintain the above. That is, by setting the ratio of the contact area B (cm ² ) between the ink and the air to the amount of ink A (cm ³ ) in the ink tank to be B≦0.5A cm ² , the degree of degassing can be reduced to a practically acceptable range. can be suppressed.

With gel ink (phase change ink), when the heating of the ink tank is stopped, the temperature of the ink drops and the ink solidifies (gels), convection is suppressed, and dissolution in the atmosphere is suppressed. Normally, when the inkjet recording apparatus is stopped, the heating of the ink tank is also stopped, so that the gel ink is solidified and the decrease in the degree of degassing is suppressed. For this reason, as in the above measurement conditions, if the degree of degassing is maintained at 80% or more under the conditions in which the sol-state ink is convected by heating for 7 days, degassing in the ink tank is within the practical range. It is possible to sufficiently suppress the generation of air bubbles in the head portion due to the decrease in viscosity.

Therefore, by providing an ink tank in which the contact area ^Bcm2 between the ink and the atmosphere satisfies B≦0.5A in the ink amount (volume) ^Acm3 within the specified range of the ink tank, the decrease in the degassing degree of the ink is suppressed. and back pressure control can be realized. Further, in the ink tank, by controlling the contact area B cm ² between the ink and the atmosphere in the ink amount (volume) A cm ³ within the specified range to B, ≤ 0.5 A, the decrease in the degassing degree of the ink is suppressed. , back pressure control can be realized.

[Example 2: Decrease in degassing degree of ink due to ink volume]
Next, under the condition that the ratio of the contact area B (cm ² ) to the ink volume A (cm ³ ) is constant at B=0.5A, the ink volume A (cm ³ ) and the contact area B (cm ² ) are Ink tanks containing different inks were prepared, and how the degree of degassing of the ink in the ink tanks decreased over time was measured.

FIG. 9 shows the conditions (conditions 1 to 4) of the ink volume A (cm ³ ) of the ink tank and the contact area B (cm ² ) between the ink and the air. Except for the ink volume A (cm ³ ) and the contact area B (cm ² ) between the ink and air, the same apparatus and method as those used for measuring the degree of degassing in Example 1 were used.

FIG. 10 shows a table of the measurement results of the degree of ink degassing. Also, a graph is shown in FIG.
As shown in FIGS. 10 and 11, under conditions where the ratio of the contact area B (cm ² ) between the ink and the air in the ink volume A (cm ³ ) is the same, the ink volume A (cm ³ ) and the contact area B (cm 3 ) ² ) changes, the degree of deaeration similarly decreases.
Furthermore, even if the ink volume A (cm ³ ) and the contact area B (cm ² ) change, the ratio of the contact area B (cm ² ) between the ink and the atmosphere in the ink volume A (cm ³ ) is B=0. At 0.5 A, the degassing degree of the ink after holding at 80° C. for 7 days can be maintained at 80% or more.

From this result, regardless of the ink volume A ^{(cm 3 )} in the ink tank and the contact area B (cm ² ) between the ink and the atmosphere, the contact area B ( cm ² ) is B≤0.5A, the degree of degassing after 7 days can be maintained at 80% or more. Thus, in the ink tank in which the ink and the atmosphere are brought into contact for back pressure control, the contact area B (cm ² ) between the ink and the atmosphere is 0.5 A or less with respect to the ink volume A (cm ³ ). Thereby, the decrease in the deaeration degree of the ink can be suppressed to a sufficiently practical range. As a result, it is possible to realize an inkjet recording apparatus capable of suppressing a decrease in the degree of ink degassing and controlling the back pressure.

[Example 3: Decrease in degassing degree of ink due to degassing temperature]
Next, under conditions where the temperature of the ink in the ink tank and the temperature of the ink degassing device located upstream of the ink tank are different, the decrease in the degree of degassing of the ink in the ink tank over time is measured. did.

The ink amount A (cm ³ ) in the ink tank is 30 (cm ³ ), the contact area B (cm ² ) between the ink and the atmosphere is 15 (cm ² ), and the contact area B (cm 3 ) at the ink amount A (cm ³ ) ² ), an ink tank having a ratio of B=0.5 Acm ² was prepared. The ink jet recording apparatus was set so that the ink temperature in the ink degassing device was 80.degree. C. or 95.degree. C. and the ink temperature in the ink tank was 80.degree.
For the conditions other than the above, the same apparatus and method as those used for measuring the degree of degassing in Example 1 were used.

FIG. 12 shows the measurement results of the degree of ink degassing.
As shown in FIG. 12, the ink temperature in the ink degassing device is 95° C. (broken line in FIG. 12) than the ink temperature in the ink degassing device is 80° C. (solid line in FIG. 12). However, the decrease in degassing degree over time became gradual.
The higher the temperature of the ink, the easier it is for the amount of dissolved oxygen in the ink to decrease. Therefore, by raising the degassing temperature of the ink, the amount of oxygen contained in the ink supplied to the ink tank is reduced. In this way, by reducing the amount of dissolved oxygen in the ink supplied to the ink tank in advance, the amount of dissolved oxygen in the ink can be reduced even after the ink is held in the ink tank for a certain period of time under conditions of contact with the atmosphere. .

As described above, the higher the temperature of the liquid, the smaller the saturated dissolved oxygen amount. At this time, the gas supersaturated due to the decrease in the saturated dissolved oxygen amount due to the rise in temperature forms bubbles in the ink. Bubbles generated in the ink cause cavitation immediately when the ink is ejected from the head section, which poses a problem. In particular, in the ink chamber of the head portion having the piezo element, the ink is repeatedly pressurized and depressurized continuously. At this time, if minute air bubbles are present in the ink, the dissolved gas moves to the air bubbles when the ink is decompressed, and the air re-dissolves from the air bubbles into the ink when the ink is pressurized. When such pressurization and depressurization are repeated, due to the relationship of the surface area of the bubbles, the flow of the dissolved gas to the bubbles prevails, so the bubbles grow. Then, when the bubbles grow to a certain size, cavitation occurs in the head portion. The flow of the dissolved gas into the bubble is proportional to the partial pressure of the dissolved gas in the ink (dissolved gas concentration/saturated dissolved gas concentration).

As described above, from the viewpoint of the degree of degassing, the saturated dissolved oxygen amount increases as the ink temperature decreases. temperature of the deaerator). Alternatively, in the ink degassing device, it is preferable to degas the ink at a temperature higher than the temperature in the ink flow path after degassing such as the ink tank and the head section. Further, the ink degassing temperature in the ink degassing device and the temperature of the ink flow path after degassing such as the ink tank and the head are controlled by the control unit so that the ink temperature satisfies the above relationship. good too.

[Example 4: Decrease in degassing degree of ink due to temperature difference between ink and atmosphere]
Next, under conditions where the temperature of the ink in the ink tank differs from the temperature of the air, the decrease in the degassing degree of the ink in the ink tank over time was measured. The atmospheric temperature was changed to 40°C, 50°C, 60°C, and 70°C while the ink temperature in the ink tank was set to 80°C or 90°C. As a result, the degassing degree of the ink was measured by setting the temperature difference between the ink and the air in the ink tank to 20°C, 30°C, or 40°C.
For the conditions other than the above, the same apparatus and method as those used for measuring the degree of degassing in Example 1 were used.

FIG. 13 shows the measurement results of the degree of ink degassing.
As shown in FIG. 13, regardless of whether the ink temperature is 80.degree. C. or 90.degree. On the other hand, regardless of whether the ink temperature is 80.degree. C. or 90.degree. That is, although there is a slight difference in how the degree of degassing decreases depending on the ink temperature (80° C., 90° C.), the larger the temperature difference between the ink and the atmosphere, the more easily the degassing degree of the ink decreases. rice field. From the above measurements, it is preferable that the temperature difference between the ink in the ink tank and the atmosphere is 30° C. or less in order to maintain the degree of degassing at 80% or more after 7 days.

Even if the ink temperature in the ink tank is different, if the temperature inside the ink tank is maintained at a constant temperature, the influence of the difference in ink temperature on the convection is small. On the other hand, the temperature difference between the ink temperature and the atmosphere greatly affects the ink convection in the ink tank regardless of the ink temperature. When the temperature difference between the ink and the atmosphere increases, the ink temperature tends to change depending on the temperature of the atmosphere. Therefore, a temperature difference is likely to occur between the portion of the ink in the ink tank that is in contact with the atmosphere and the other portion. Therefore, as the temperature difference between the ink and the atmosphere increases, convection tends to occur in the ink tank, and the degree of deaeration of the ink tends to decrease.

The present invention is not limited to the configurations described in the above embodiments, and various modifications and changes are possible without departing from the configuration of the present invention.

10 medium supply unit 11 supply tray 12 feeder board 20 image forming main unit 21 transfer unit 22 image forming drum 23 head unit 24 irradiation unit 25 delivery unit 26 ink tank 27 back pressure adjustment unit 29 ink degassing device 30 medium discharge unit 31 discharge tray 40 control unit 41 CPU 42 RAM 43 ROM 44 memory 50 ink storage unit 51 first ink feeding unit 52 second ink feeding Section 53 Deaerator Heating Section 54 Ink Tank Heating Section 55 Head Heating Section 56 Liquid Level Sensor 57 Ink 58 Lid Member 61 Communication Section 62 Operation Display Section 69 Bus 71 Transport Drive Section 74 Irradiation drive part 100 Ink jet recording device 121, 122, 252, 253 Rollers 123, 254 Belt 211 Swing arm part 212 Transfer drum 221 Drum heater 230 Ink jet head 241 Light shielding plate 251 Transfer roller 731 Head Drive part

Claims (9)

an ink degassing device for degassing ink;
a head unit for ejecting the ink;
When Acm ³ is the amount of ink within a specified range and Bcm ² is the contact area between the ink and the air at the ink amount A, which is provided downstream of the ink degassing device and accommodates the supplied ink. 2, an ink tank with B≦0.5A;
an ink tank heating unit for heating the ink in the ink tank;
a back pressure adjusting unit that adjusts the back pressure of the ink in the ink tank;
a control unit that controls the ink tank heating unit so that the temperature of the ink in the ink tank is equal to or lower than the temperature of the ink degassing device and the temperature difference from the temperature of the atmosphere is 30° C. or lower. Device. The inkjet recording apparatus according to claim 1, further comprising a head heating section for heating the head section. an ink storage unit for storing the ink arranged upstream of the ink degassing device;
3. The inkjet recording apparatus according to claim 1, further comprising an ink feeding section that feeds the ink from the ink storage section to the ink degassing device. The inkjet recording apparatus according to any one of claims 1 to 3, further comprising an ink amount detection section for detecting the amount of ink contained in the ink tank. The controller controls the amount of ink in the ink tank so that B≦0.5A.
The inkjet recording apparatus according to claim 4. 6. The inkjet recording apparatus according to any one of claims 1 to 5, further comprising an atmosphere shielding portion for partially shielding contact between the ink and the atmosphere in the ink tank. 7. The inkjet recording apparatus according to claim 6, wherein the air blocking section is a lid member covering the ink. The inkjet recording apparatus according to claim 7, wherein the cover member constitutes an ink amount detection section for detecting the amount of ink contained in the ink tank. an ink degassing device for degassing ink; a head portion for ejecting the ink; an ink tank provided downstream of the ink degassing device for containing the ink; A control method for an inkjet recording apparatus comprising an ink tank heating section for heating and a back pressure adjusting section for adjusting the back pressure of the ink in the ink tank,
The ink in the ink tank is such that B≦0.5A, where Acm ³ is the volume of the ink in the ink tank, and Bcm ² is the contact area between the ink and the air at the ink amount A. control the amount,
The ink tank heater is controlled so that the temperature of the ink in the ink tank is equal to or lower than the temperature of the ink degassing device and the temperature difference from the temperature of the atmosphere is 30° C. or lower.
A control method for an inkjet recording apparatus.

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